The image forming device represented by a color printer and the like generally includes a three-dimensional lookup table (hereinafter abbreviated as “LUT”) for converting a multi-dimensional color signal input from a host computer etc. to another multi-dimensional color signal and outputting such color signal, where a suitable color conversion process can be performed and a desired image output process can be performed by referencing the LUT.
Specifically, the LUT can be used in a color data conversion method of generating second color data contained in a printer color gamut (second color gamut) in a L*a*b* color space, (hereinafter “L*a*b* space”) (L* is a number that represents lightness of color; a* represents position of color between red/magenta and green; and b* represents the color position between yellow and blue), corresponding to a Cyan, Magenta, and Yellow color space, (hereinafter “CMY space”), of a printing device (second device) such as a color printer from first color data contained in a display color gamut (first color gamut) in the L*a*b* space generally corresponding to an Red, Blue, Green color space, (hereinafter “RGB space”) of a color display device (first device) such as a CRT display.
The following method is purported to be for the related art of such color data conversion method.
A method including a virtual color gamut obtaining process, a color data conversion process, and a color data generating process is proposed.
The virtual color gamut obtaining process converts one or more values of a brightness value, a chroma value, and a hue angle value of the second color gamut, and obtains an extended virtual color gamut including at least all the brightness values of the first color gamut.
The color data conversion process changes one or more values of the brightness value, the chroma value, and the hue angle value with respect to the color data of the first color gamut, that is, not contained in the virtual color gamut and obtains third color data contained in the virtual color gamut.
The color data generating process performs an inverse conversion on the second color gamut in the virtual color gamut obtaining process, and performs the conversion on the third color data obtained in the color data changing process. The process generates second color data.
There is another method relating to a color gamut compression device for compressing a color gamut. The color gamut is compressed by converting a color expressed by an input system information equipment to a color within a color gamut reproducible by an output system information equipment. The color gamut compression device includes a converging point calculation unit for calculating a converging coordinate. Calculation of the coordinate is based on an arbitrary point that has the same hue as a color that is within a color gamut of the output system information equipment and a chromatic color as a converging point. The calculation uses the arbitrary point when a digital signal value of the input system information equipment corresponds to a determined color. The color is determined based on the color of the input system information equipment reproduced with the output system information equipment. Pursuant to the technique for compressing a color gamut, the device further comprises a first compression point calculating unit for calculating a compression point as coordinate of an arbitrary point on a substantially straight line. The substantially straight line connects the converging point and a point, corresponding to the color of the input system information equipment and being within the color gamut of the output system information equipment as a compression point. The color gamut compression device also comprises, in accordance with the color gamut compression technique, a compression unit for converting the color of the input system information equipment to a color corresponding to the compression point calculated by the first compression point calculating unit.
Furthermore, another method relates to matching color performed between a first image equipment and a second image equipment having different color reproduction ranges. According to this method, a color gamut color compression unit for performing color gamut compression links a color in the color gamut of the color of the first image equipment and a color in the color gamut of the color of the second image equipment. A color gamut outermost contour color gamut compression unit links a color gamut outermost contour color of the color of the first image equipment and a color gamut outermost contour color of the color of the second image equipment. A lookup table creating unit creates a lookup table to perform color conversion on a color of the second image equipment using a color signal calculated by the color gamut color compression unit and the color gamut outermost contour compression unit. Finally according to this method, a color conversion processing unit performs color conversion on the color of the second image equipment using the lookup table from the lookup table creating unit are arranged.
There is another method relating to a color gamut compression method for compressing input image data of a first color gamut into a second color gamut in order to obtain output image data. The method includes a compressing step of compressing a value of the color data not contained in the second color gamut from the color data of each color in the first color gamut into a value of the color data contained in the second color gamut through a predetermined compression calculation. This method further comprises a tone generating step of having the values of a plurality of color data of the same value after the compression step as values of different color data in the second color gamut.
In the related methods, there is a high possibility that the tones in the same hue may lose continuity when compression of the color gamut is performed.